Extruded plastics netting

ABSTRACT

An extruded orientated tubular plastic mesh or net for packaging purposes comprising an inner set or layer of spaced parallel orientated strands extending in a helix around the tube, an outer set or layer of similarly spaced parallel orientated strands extending in an equal angle but opposite helix around the tube, the inner and outer sets or layers of strands being unconnected at their crossing points and a third set or layer of spaced strands, more orientated and attenuated than the helical strands, interconnecting the inner and outer sets or layers of helical strands along lines of connection points parallel to the tube axis, each strand of the third set or layer having alternate connection along its length with the outer sides of the strands of the inner set and the inner set of the strands of the outer set, each third set strand extending from connection point to adjacent connection point along a looped untensioned path.

1 11 3,744,529 14 July 10,1973

1 EXTRUDED PLASTICS NETTING [75] Inventors: Jose Mas Jorda; Jacinto Fort Farre; Francisco Gutierrez Espinosa, all of Cardedeu (Barcelona), Spain [73] Assignee: Netlon (P.T.A.)Limited,Lancashire,

' England [22] Filed: Apr. 8, 1971 [21] Appl. No.: 132,432

30 Foreign Application Priority Data .Apr. 9, 1970 Great Britain 17,008/70 52 US. Cl 138/125, 138/137, 156/167, 156/180, 161/58, 161/89, 161/143, 264/177 511 1m. (:1. 865d 29/04,'D041i 3/16 [58] Field of Search 161/70,57, 143,

l6l/DlG-. 6, 109, 89, 58; 156/167, 180, 175; 264/DIG. 8,176, 210,176 F, 177 F, 210 F; 138/125, 130, 144

3,518,720 7/1970 Fairbanks 156/167 X 3,525,785 8/1970 Fairbanks 156/167 X 3,562,046 -2/l971 Guy 156/167 3,592,718 7/1971 Fairbanks 156/167 X FOREIGN PATENTS OR APPLICATIONS 836,555 6/1960 Great Britain 939,588 10/1963 Great Britain Primary Examiner-Harold Ansher Attorney-Holman & Stern [57] ABSTRACT An extruded orientated tubular plastic mesh or net for packaging purposes comprising an inner set or layer of spaced parallel orientated strands extending in a helix around the tube, an outer set or layer of similarly spaced parallel orientated strands extending in an equal angle but opposite helix around the tube, the inner and outer sets or'layers of strands being unconnected at their crossing points and a third set or layer of spaced strands, more orientated and attenuated than the helical strands, interconnecting the inner and outer sets or layers of helical strands along lines of connection points parallel to the tube axis, each strand of the third set or layer having alternate connection along its length with the outer sides of the strands of the inner set and the inner set of the strands of the outer set, each third set strand extending from connection point to adjacent connection point along a looped untensioned path.

2 Claims, 7 Drawing Figures PATENIEDJUL 1 0191s sneer 1 or 4 F l G. I.

' INVENTOR JOSE MAS JORUA ET M.

PAIENIEB M E v .744.529-

snmaura FL "/I 1'3 INVENTOR JOSE MAS JORDA 61 AL EXTRUDED PLASTICS NETTING BACKGROUND OF THE INVENTION This invention relates to a tubular net for packaging purposes (particularly as described hereinafter) of the type comprising two sets of parallel extruded plastic strands extending in opposite helices around the tube, the tubular net having been stretched longitudinally in rope form to cause molecular orientation of the plastic in the net strands. Net of the above type may be made, for example, according to the method, and by the apparatus similar to that shown in US. Pat. No. 2,919,467 wherein two concentric sets of spaced extrusion die orifices are caused to counter-rotate while being fed with plastic under pressure, the die orifices being formed as open slots or by converging sets of bores opening onto the die face either as closely spaced discrete full orifices or as orifices opening partly onto the die face and partly onto the rotational bearing face of the die all in known manner.

Packaging as referred to in this specification is the packaging of one or more, usually a number, of goods or articles within the net tube by closing the tube with a clip or tie, loading the article or articles into the tube through the tube, closing the tube behind the article or articles by a clip or tie and severing the completed pack from the remaining net tube. Produce such as fruit or vegetables lend themselves particularly to packagingin this manner and high packaging speeds are obtained by loading a long length of net tube concertina-ed or gathered in folds onto an inclined feed tube down which articles to be packed are fed. The net tube may be loaded in rope form direct on to the feed tube of the packaging machine or the net may be pre-sleeved on a paper or card core or support which can be slid over the feed tube. In order to obtain maximum efficiency it is desirable to load the packaging machine with as long a length of concertina-ed or gathered in folds net as possible.

Such roped net packaging is well known and in addition to extruded plastic nets other structures commonly used are knitted cotton, rayon or plastic monofilament nets.

By the term plastic as used herein, is meant:

a. a synthetic organic thermoplastic polymer material capable of melt or compression extrusion in a molten state through dies and settable by a cooling medium on issuance from the dies. Suitable thermoplastic materials include polyamides or superpolyamides, such as nylon; polyesters; polyvinylchloride and copolymers thereof with vinylacetate or vinylidine chloride; and polyolefins and the like; or

b. natural organic macromolecular materials such as cellulose chemically modified e.g., by esterification to render them thermoplastic, such as cellulose acetate.

This definition is subject to the above materials being safe and suitable for use in the methods, or for the product, described herein.

Extruded plastic nets produced as set out above have the intersecting sets of helical strands joined to each other at each crossing point and the double thickness of plastic at each crossing point usually remains largely unstretched and unorientated when the net is stretched in rope form so that small thicker unorientated masses of plastic or knots remain.

Extruded plastic nets as described in the preceeding paragraph is a strong and satisfactory structure for packaging particularly in the form of sacks or bags although there is a tendency-for tear lines to develop along the net strands caused by stresses being concentrated at the transition points between the stretched and orientated plastic strands and the thicker unorientated junctions or knots". Also such nets have considerable radial elasticity or spring caused by the stiff' ness of the bonded net intersections which can cause the net to bind on the feed tube of the packaging machine or to crush the paper or card core or support of a pre-sleeved net length. The bonded net intersections of such nets also prevent the net tube from being packed up tight with maximum density on the feed tube or pre-sleeve core or support.

These disadvantages do not occur, or occur to a much less degree, in knitted nets, which, are limp or dead and therefore have the further advantage of softness thereby minimizing damage to soft-skinned fruit such as apples.

OBJECTS AND SUMMARY OF THE lNVENTION It is an object of the present invention to provide an improved tubular plastic packaging net by an extrusion process, which has the advantageous qualities of a knitted net but which is manufactured in a single stage direct from the raw material. Among the further objects of the present invention are the following: an improved tubular plastic packa g ing net produced by extrusion, in which:

a. no bulky intersections or knots are present,

b. stresses applied to the net concentrate, and dissipate, themselves along the lines of the helical strands,

c. the two sets of helical strands are not interconnected dynamically in the plane of the net,

d. the helical strands are more uniformly stretched and molecularly orientated throughout their length,

e. as a packaging material, particularly for delicate skinned fruits, improved contouring of the net over the curved surface of the fruit is obtained, giving a greater distribution of stress over the surfaces thereby lessening the liability of damage to the fruit and -reducing stress concentrations in the net itself.

The invention consists in an extruded orientated tubular plastic mesh or net for the purposes indicated comprising an inner set or layer of spaced parallel orientated strands extending in a helix around the tube, an outer set or layer of similarly spaced parallel orientated strands extending in an equal angle but opposite helix around the tube, the inner and outer sets or layers of strands being unconnected at their crossing points and a third set or layer of spaced strands, more orientated and attenuated than the helical strands, interconnecting the inner and outer sets or layers of helical strands along lines of connection points parallel to the tube axis, each strand of the third set or layer having alternate connection along its length with the outer sides of the strands of the inner set and the inner sides of the strands of the outer set, and each third set strand extending from connection point to adjacent connection point along a looped untensioned path.

The invention further consists in an extruded orientated tubular plastic meshs or net according to the preceding paragraph in which the junctions of the third set of strands with the strands of the inner and outer sets are positioned substantially midway between adjacent crossing points of the inner and outer sets of strands.

The invention still further consists in an extruded orientated tubular plastic meshs or net according to the preceding paragraph wherein the third set strands extend between connections with the inner and outer set strands either:

a. on each side of every crossing point of the inner and outer set strands, or

b. on one side only of every crossing point.

By this arrangement, the inner and outer sets of strands are capable of independent movement along their lengths, transversely of their lengths and away from each other transverse to the plane of the net, this freedom of movement giving rise to the objects and advantages of the present invention, more particularly:

a. the soft, limp or dead handle to the net,

b. reduction or elimination of radial elasticity of any effective degree,

0. concentration and dissipation of applied stresses along the lines of the helical strands,

d. improved contouring of the net over the curved surfaces of packaged articles such as fruit,

e. greater densification potential by concertina-ing or the gathering into folds of the net; for packaging feed tube or sleeve loading.

The improved net according to the present invention is produced by extruding a suitable plastic from three concentric adjacent sets of spaced die orifices, an inner set, an intermediate set and an outer set, the inner and outer sets counter-rotating at equal speeds to give equal but opposite helix angles to the inner and outer strands extruded therefrom and the intermediate set being stationary and the die orifices thereof positioned so that they are not in radial register with the die orifices of the inner set and outer set as the latter pass in radial register. The resultant three strand net, having two sets of strands extending helically and oppositely around the net tube and the third set extending in the machine direction, i.e., parallel to the tube axis or direction of extrusion, is passed into a cooling-bath and set and thence passed to a stretching device which firstly causes the intermediate or third set of strands to stretch whereby the net takes up a roped form only then enabling a degree of stretch to take place in the other (helical) strands, whereby the intermediate or third set of strands are always considerably more stretched than theother (helical) strands, hence the looped configuration of the intermediate or third strands when the net tube is opened up."

The inner and outer helical strands are not directly connected one to another and after stretching has taken place and the net tube opened up, the intermediate strands which link the inner strands loosely to the outer strands are in a looped or wavy untensioned configuration for the reason mentioned above.

A three strand net extruded from three concentric adjacent sets of dies, the intermediate set of which is stationary, has been previously proposed in-U.S. Pat. No. 3,227,184, but this net is not subjected to orientation by stretching and inherently required that no stretching takes place since each set of strands must be taut and capable of tensile load bearing including and especially the intermediate or longitudinal strands, the object of this prior three strand net construction being to provide greater dimensional stability than two strand diamond net, whereas the net structure of the present 4 invention deliberately has as little dimensional stability as posible. Thus to stretch the roped nets of US. Pat. No. 3,227,184 would be contrary to all the teaching of that patent.

According to the present invention, when the orientated roped net is opened up for sleeving or loading on to the feed tube of a packaging machine, the resultant relative movement of the helical strands causes the intermediate strands to adopt a looped formation, in which state they can have no effect on the stability of the opened mesh structure of the net tube and since neither the outer nor the inner strands are at any time or place joined together through common joints or intersections with the intermediate strands, the result is a totally unstable diamond mesh structure.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a portion of oriented net according to the present invention,

FIG. 2 is a portion of oriented net as in FIG. 1 on an enlarged scale,

FIG. 3 is a perspective view of the cross-over of an inner strand and an outer strand and a pair of intermediate strands interconnecting them,

FIG. 4 is a side elevation of the crossover shown in FIG. 3,

FIG. 5 is a diagram showing the independent movement of crossing inner and outer strands,

FIG. 6 is a sectional side elevation of the dies for extruding the net from which the oriented net according to the present invention is formed, and

FIG. 7 is a sectional side elevation on an enlarged scale of the die lips as shown in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION The oriented net according to one form of the present invention comprises (FIGS. 1 and 2) inner strands l, outer strands 2 and intermediate strands 3 interconnecting the strands 1 and 2. The intermediate strands 3 are stretched more than the innerand outer strands l and 2 when the net in tubular roped form (as previously described), is stretched after extrusion and in consequence the strands 3 are always much thinner and more flexible than the strands 1 and 2, but since it is important that the strands 3 exert minimal physical forces on the net structure, the strands 3, as cast i.e., before stretching, are preferably thinner or finer than the inner and outer strands 1 and 2 so that it is ensured that the strands 3 are very much thinner than the inner and outer strands l and 2. Since the intermediate strands 3 are also longer, due to the greater stretch, than the strands l and 2 they adopt a looped formation between their junction points 4 and 5 with the inner and outer strands l and 2 respectively, which junction points 4 and 5 lie on lines running parallel to the net tube axis X X (FIG. 2). Where the inner and outer strands l and 2 cross one another as at 6 there is no joint or connection between them and in consequence the strands l and the strands 2 can move independently as shown by the arrows in FIG. 5 (the intermediate strands 3 not being shown in this drawing).

The three strand (inner, outer and intermediate) tubular net to be stretched according to the present in-' vention is extruded from a die head (FIG. 6) having three concentric circular die lips 10, 1-1 and 12 (see FIG. 7) of which the die lip 10 extrudes the inner strands l, the die lip 11 the outer strands 2 and the die lip 12 the intermediate strands 3. The die lips and 11 are counter-rotated at equal speed by means not shown and the die lip 12 is held stationary on a fixed sleeve 13 surrounding a shaft 14 of the inner die lip 10.

The die lips 10, 11 and 12 are formed, in known manner, with circumferentially spaced die orifices in the form, as shown in FIG. 7, of die slots 15, 16, 17 but these die orifices may also be formed in known manner by bores (not shown).

Where intermediate strands 3 are disposed on each side of the crossing points of the inner and outer strands 1 and 2, the die lip 12 has twice as many die slots or other die orifices 17 as the inner or outer die lips 10 or 11; likewise where intermediate strands 3 are disposed on one side only of every crossing point, the' die lip 12 has the same number of slots or orifices 17 as the other die lips.

The plastic feeds to the die lips 10, 11, 12 and the rostretched in rope form (as previously described) to become the tubular oriented net according to the present invention having the improved and special qualities, properties and advantages set forth hereinbefore.

We claim:

1. An extruded orientated tubular plastic mesh or net for packaging purposes comprising an inner set or layer of spaced parallel orientated strands extending in a helix around the tube, an outer set or layer of similarly spaced parallel orientated strands extending in an equal angle but opposite helix around the tube,'the inner and outer sets or layers of strands being unconnected at their crossing points and a third set or layer of spaced strands, more orientated and attenuated than the helical strands, interconnecting the inner and outer sets or layers of helical strands along lines of connection points parallel to the tube axis, each strand of the third set of layer having alternate connection along its length with the outer sides of the strands of the inner set and the inner sides of the strands of the outer set, each third set strand extending from connection point to adjacent connection point along a looped untensioned path.

2. The extruded orientated tubular plastic mesh or net as claimed in claim 1 in which the junctions of the third set of strands with the strands of the inner and outer sets are positioned substantially midway between adjacent crossing points of the inner and outer sets of strands. 

1. An extruded orientated tubular plastic mesh or net for packaging purposes comprising an inner set or layer of spaced parallel orientated strands extending in a helix around the tube, an outer set or layer of similarly spaced parallel orientated strands extending in an equal angle but opposite helix around the tube, the inner and outer sets or layers of strands being unconnected at their crossing points and a third set or layer of spaced strands, more orientated and attenuated than the helical strands, interconnecting the inner and outer sets or layers of helical strands along lines of connection points parallel to the tube axis, each strand of the third set of layer having alternate connection along its length with the outer sides of the strands of the inner set and the inner sides of the strands of the outer set, each third set strand extending from connection point to adjacent connection point along a looped untensioned path.
 2. The extruded orientated tubular plastic mesh or net as claimed in claim 1 in which the junctions of the third set of strands with the strands of the inner and outer sets are positioned substantially midway between adjacent crossing points of the inner and outer sets of strands. 